The present invention relates generally to fuel management systems for internal combustion engines, and more specifically to such systems for controlling transient particulate emissions by controlling a transient fuel-to-oxygen, or equivalence, ratio.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). Particulate emissions are likewise generally undesirable, and the amount of transient particulate emissions produced by an engine is largely a function of the transient peak overall fuel-to-oxygen, or equivalence, ratio ("PHgr"). Unfortunately, both problems are aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted NOx emissions involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold.
Constraining particulate emissions, on the other hand, requires carefully controlling the equivalence ratio ("PHgr"), particularly during transient operating conditions. However, no systems are currently known for accurately estimating in-cylinder oxygen content in dynamic fuel/O2 environments that are generally characteristic of EGR-based systems. Accordingly, no accurate equivalence ratio-based fuel control systems are known to exist. What is therefore needed is a system for accurately determining in-cylinder oxygen content, and for controlling the fuel-to-oxygen, or equivalence, ratio "PHgr" based on this information as well as on other current operating conditions to thereby minimize transient particulate emissions while optimizing transient torque capability in a dynamic fuel/O2 environment that is characteristic of EGR-based systems.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, an equivalence ratiobased system for controlling transient fueling in an internal combustion engine comprises an engine speed sensor producing an engine speed signal indicative of rotational speed of an internal combustion engine, means for determining a quantity of oxygen trapped within a number of cylinders of the engine and producing an oxygen estimate corresponding thereto, and a control circuit producing a fueling command for fueling the engine and determining a maximum equivalence ratio value based on the fueling command and the engine speed signal, the control circuit limiting the fueling command based on the maximum equivalence ratio and the oxygen estimate.
In accordance with another aspect of the present invention, an equivalence ratio-based system for controlling transient fueling in an internal combustion engine comprises an engine speed sensor producing an engine speed signal indicative of rotational speed of an internal combustion engine, means for determining a residual mass value corresponding to a mass of residual gases trapped within a number of cylinders of the engine, means for producing a fueling command for fueling the engine, means responsive to the residual mass value, the engine speed signal and the fueling command for determining a quantity of oxygen trapped within the number of cylinders of the engine and producing an oxygen value corresponding thereto, and a control circuit limiting the fueling command based on the engine speed signal, the fueling command and the oxygen value.
In accordance with yet another aspect of the present invention, an equivalence ratio-based method for controlling transient fueling in an internal combustion engine comprises the steps of sensing rotational speed of an internal combustion engine and producing an engine speed signal corresponding thereto, determining a maximum equivalence ratio value based on an engine fueling command and the engine speed signal, determining a quantity of oxygen trapped within a number of cylinders of the engine and producing an oxygen value corresponding thereto, and limiting fuel supplied to the engine command based on the maximum equivalence ratio and the oxygen value.
In accordance with still another aspect of the present invention, an equivalence ratio-based method for controlling transient fueling in an internal combustion engine comprises the steps of sensing rotational speed of an internal combustion engine and producing an engine speed signal corresponding thereto, determining a residual mass value corresponding to a mass of residual gases trapped within a number of cylinders of the engine, producing a fueling command for fueling the engine, determining a quantity of oxygen trapped within the number of cylinders of the engine based on the engine speed, the residual mass value and the fueling command and producing an oxygen value corresponding thereto, and limiting the fueling command based on the engine speed signal, the fueling command and the oxygen value.
One object of the present invention is to provide a fueling control system for minimizing particulate emissions while optimizing engine output torque capabilities under transient operating conditions.
Another object of the present invention is to provide such a system for achieving the foregoing object in a dynamic fuel-oxygen environment characteristic of EGR-based systems.
Still another object of the present invention is to provide a fuel control system operable to achieve the foregoing objects by controlling a maximum fuel-to-oxygen, or equivalence, ratio ("PHgr") based on a computed amount of oxygen trapped within a number of cylinders of the engine as well as on other engine operating conditions.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.